Extension of the EZSMT Software System For Non-tight Constraint Answer Set Programs

Answer set programming (ASP) is a programming language that plays a critical role in the development of software applications in areas of science, humanities, and industry. Yet, it is faced with some challenges. Therefore, researchers develop a related paradigm called constraint answer set programming (CASP) to tackle several issues of ASP tools. Recently, a method is proposed to find solutions to CASP programs by using satisfiability modulo theories (SMT) solvers. SMT solvers are high-performance systems stemming from the software verification community. This SMT-based approach is implemented in a system called EZSMT, which often outperforms its peers. Yet, it has several limitations. For instance, it is unable to process a large class of programs called non-tight . This restriction does not allow users to express, for example, reachability relations between cities connected by roads on a map. Solving non-tight programs is important, because they are crucial in many applications. In this work, we extend EZSMT for non-tight input. Our main contribution is designing an extension, which adds additional requirements into non-tight programs so that SMT solvers can be called to compute solutions correctly. We also extend the architecture of original EZSMT, in order to allow computation of multiple solutions. Our experimental analysis shows that the extended EZSMT system is a viable tool when being compared to state-of-the-art CASP solvers CLINGCON and EZCSP. In summary, we believe that, by making clear the translation of arbitrary CASP programs to SMT, our work will boost the cross-fertilization between the two areas

SMT-Based Answer Set Solver CMODELS(DIFF) (System Description)

Many answer set solvers utilize Satisfiability solvers for search. Satisfiability Modulo Theory solvers extend Satisfiability solvers. This paper presents the CMODELS(DIFF) system that uses Satisfiability Modulo Theory solvers to find answer sets of a logic program. Its theoretical foundation is based on Niemala\u27s characterization of answer sets of a logic program via so called level rankings. The comparative experimental analysis demonstrates that CMODELS(DIFF) is a viable answer set solver

Computation of the field in an axial gap, trapped-flux type superconducting electric machine

The Bulk Superconductivity Group at the University of Cambridge is currently investigating the use of high temperature superconductors in wire and bulk form to increase the electrical and magnetic loading of an axial gap, trapped flux-type superconducting electric machine. The use of superconducting materials in electric machines can lead to increases in efficiency, as well as power density, which results in reductions in both the size and weight of the machine. In this paper, the authors present a method to compute the field in such an electric machine generated by an array of fully magnetized bulk superconductors. Analytical expressions are derived for the field that would exist in the coil region of the motor, which will act as a powerful tool for carrying out parametric analysis of the motor’s design and performance.This work was supported in part by a Royal Academy of Engineering Research Fellowship and by the China Scholarship Council.This is the accepted manuscript. The final version is available from IEEE at http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=6945871

Quantum electric-dipole liquid on a triangular lattice

Geometric frustrations and quantum mechanical fluctuations may prohibit the formation of long-range ordering even at the lowest temperature, and therefore liquid-like ground states could be expected. A good example is the quantum spin liquid in frustrated magnets that represents an exotic phase of matter and is attracting enormous interests. Geometric frustrations and quantum fluctuations can happen beyond magnetic systems. Here we propose that quantum electric-dipole liquids, analogs to quantum spin liquids, could emerge in frustrated dielectrics where antiferroelectrically coupled small electric dipoles reside on a triangular lattice. The quantum paraelectric hexaferrite BaFe12O19, in which small electric dipoles originated from the off-center displacement of Fe3+ in the FeO5 bipyramids constitute a two-dimensional triangular lattice, represents a promising candidate to generate the anticipated electric-dipole liquid. We present a series of experimental evidences, including dielectric permittivity, heat capacity, and thermal conductivity measured down to 66 mK, to reveal the existence of a nontrivial ground state in BaFe12O19, characterized by itinerant low-energy excitations with a small gap, to which we interpret as an exotic liquid-like quantum phase. The quantum electric-dipole liquids in frustrated dielectrics open up a fresh playground for fundamental physics and may find applications in quantum information and computation as well.Comment: 13 pages, 6 figure

Quantifying and monitoring functional Photosystem II and the stoichiometry of the two photosystems in leaf segments: Approaches and approximations

Given its unique function in light-induced water oxidation and its susceptibility to photoinactivation during photosynthesis, photosystem II (PS II) is often the focus of studies of photosynthetic structure and function, particularly in environmental stress conditions. Here we review four approaches for quantifying or monitoring PS II functionality or the stoichiometry of the two photosystems in leaf segments, scrutinizing the approximations in each approach. (1) Chlorophyll fluorescence parameters are convenient to derive, but the information-rich signal suffers from the localized nature of its detection in leaf tissue. (2) The gross O2 yield per single-turnover flash in CO2-enriched air is a more direct measurement of the functional content, assuming that each functional PS II evolves one O2 molecule after four flashes. However, the gross O2 yield per single-turnover flash (multiplied by four) could overestimate the content of functional PS II if mitochondrial respiration is lower in flash illumination than in darkness. (3) The cumulative delivery of electrons from PS II to P700? (oxidized primary donor in PS I) after a flash is added to steady background far-red light is a whole-tissue measurement, such that a single linear correlation with functional PS II applies to leaves of all plant species investigated so far. However, the magnitude obtained in a simple analysis (with the signal normalized to the maximum photo-oxidizable P700 signal), which should equal the ratio of PS II to PS I centers, was too small to match the independently-obtained photosystem stoichiometry. Further, an under-estimation of functional PS II content could occur if some electrons were intercepted before reaching PS I. (4) The electrochromic signal from leaf segments appears to reliably quantify the photosystem stoichiometry, either by progressively photoinactivating PS II or suppressing PS I via photo-oxidation of a known fraction of the P700 with steady far-red light. Together, these approaches have the potential for quantitatively probing PS II in vivo in leaf segments, with prospects for application of the latter two approaches in the field